Backside power rail and methods of forming the same

1. A semiconductor structure, comprising:

a source feature and a drain feature;

a vertical stack of nanostructures extending between the source feature and the drain feature;

a gate structure disposed over a bottom dielectric layer and wrapping around each of the vertical stack of nanostructures;

a backside dielectric layer underlying the bottom dielectric layer and extending continuously below the drain feature; and

a backside source contact extending through the bottom dielectric layer and the backside dielectric layer to electrically couple to the source feature.

2. The semiconductor structure of claim 1 , further comprising:

a first liner extending continuously from between the backside source contact and the backside dielectric layer to between the backside source contact and the bottom dielectric layer as well as from between the backside source contact and the bottom dielectric layer to between the source feature and the backside source contact.

3. The semiconductor structure of claim 2 , wherein the first liner comprises titanium silicon nitride, tantalum silicon nitride, or cobalt silicon nitride.

4. The semiconductor structure of claim 2 , further comprising:

a silicide layer disposed between the first liner and the source feature.

5. The semiconductor structure of claim 1 , wherein the backside dielectric layer is disposed below and in contact with the drain feature.

6. The semiconductor structure of claim 1 ,

wherein the vertical stack of nanostructures extends between the source feature and the drain feature along a direction,

wherein the bottom dielectric layer is disposed between a portion of the backside dielectric layer and a portion of the backside source contact along the direction,

wherein the bottom dielectric layer comprises a rounded corner adjacent the portion of the backside source contact.

7. The semiconductor structure of claim 1 , further comprising:

a frontside source contact disposed over the source feature, wherein the frontside source contact comprises titanium nitride, titanium, ruthenium, nickel, cobalt, copper, molybdenum, tungsten, tantalum, or tantalum nitride.

8. The semiconductor structure of claim 7 , further comprising:

a frontside silicide layer disposed between the source feature and the frontside source contact, wherein the frontside silicide layer comprises titanium silicide, titanium silicon nitride, tantalum silicide, tungsten silicide, cobalt silicide, or nickel silicide.

9. A semiconductor structure, comprising:

a backside dielectric feature;

a first drain feature disposed over the backside dielectric feature;

a backside source contact;

a source feature disposed over the backside source contact;

an isolation feature disposed between the backside dielectric feature and the backside source contact along a first direction;

a dielectric fin disposed on the isolation feature and sandwiched directly between the source feature and the first drain feature along the first direction;

a first liner disposed between the backside dielectric feature and the isolation feature; and

a second liner disposed between the backside source contact and the isolation feature.

10. The semiconductor structure of claim 9 , wherein the source feature and the first drain feature comprise silicon or silicon germanium.

11. The semiconductor structure of claim 9 ,

wherein the dielectric fin comprises a high-k dielectric material and a low-k dielectric material,

wherein the high-k dielectric material is selected from a group consisting of hafnium oxide, zirconium oxide, hafnium aluminum oxide, hafnium silicon oxide, and aluminum oxide,

wherein the low-k dielectric material is selected from a group consisting of silicon carbonitride, silicon oxycarbide, and silicon oxycarbonitride.

12. The semiconductor structure of claim 9 , wherein a composition of the first liner is different from a composition of the isolation feature.

13. The semiconductor structure of claim 9 , wherein a composition of the second liner is different from a composition of the isolation feature.

14. The semiconductor structure of claim 9 , wherein a thickness of the second liner is smaller than a thickness of the first liner.

15. The semiconductor structure of claim 9 , further comprising:

a second drain feature;

a plurality of nanostructures extending between the source feature and the second drain feature along a second direction perpendicular to the first direction; and

a gate structure wrapping around each of the plurality of nanostructures.

16. The semiconductor structure of claim 15 ,

wherein the gate structure is disposed over a bottom dielectric layer,

wherein the backside source contact is spaced apart from the bottom dielectric layer by the second liner.

17. The semiconductor structure of claim 16 , wherein a portion of the second liner extends along a rounded corner of the bottom dielectric layer.

18. A semiconductor structure, comprising:

a first epitaxial feature and a second epitaxial feature;

a plurality of nanostructures extending between the first epitaxial feature and the second epitaxial feature;

a gate structure wrapping around each of the plurality of nanostructures;

a bottom dielectric feature disposed over the gate structure;

a backside dielectric layer disposed over the first epitaxial feature; and

a backside contact disposed over the second epitaxial feature,

wherein the backside dielectric layer and the backside contact is spaced apart by a first liner adjacent the backside dielectric layer and a second liner adjacent the backside contact.

19. The semiconductor structure of claim 18 , wherein a thickness of the second liner is smaller than a thickness of the first liner.

20. The semiconductor structure of claim 18 ,

wherein the first liner is formed of an oxygen-free dielectric material,

wherein a composition of the second liner is different from a composition of the bottom dielectric feature.